Caloplaca coralloides

Ecology

Caloplaca coralloides is found at Hopkins Marine Station in Monterey
living on exposed granitic rock surfaces in the lower supralittoral zone. Very
few macroscopic organisms are living on these rocks. In this sense, C.
coralloides is taking advantage of habitat that appears to be not easily
livable. In fact, lichens are often the pioneers of inhospitable environments.
There are lichens that can survive in some of the coldest and hottest places
on earth. For example, some lichens can survive temperatures of 70 degrees
C if they are in a dry state. Additionally, many lichens can fix nitrogen
(those with cyanobacteria—C. coralloides does not) and break
up rocks, processes that over long periods of time can make the local environment
more hospitable to other organisms. The lichens on the rocks in
the supralittoral zone at Hopkins Marine Station in Monterey, CA seem to
be loosening bits of the surface of the rocks they are living on by growing
their rhizines down into little fissures in the rocks.

The only other macroscopic photosynthetic organisms growing along with C.
coralloides on the rocks directly above the intertidal zone at the
Hopkins Marine Station are other lichens; one is a small orange lichen
called Caloplaca luteominia var. luteominia. Only the
bright orange apothecia of this lichen are visible because the thallus
often grows entirely within the rock. The apothecia are mostly 0.6 to
1.2 mm in diameter.The other lichen is also crustose and growing its thallus
down into the rock. It has a grey, white and black thallus. The apothecia
have black hymenia surrounded by white. This black and white lichen was
not successfully identified. Both Caloplaca luteominia var. luteominia and
the black and white lichen grow right up next to C. coralloides and
may be primarily responsible for loosening bits of the rock by growing
their thalli down into the rock.
C. coralloides is considered a marine lichen if one uses the definitions
of “marine” and “maritime” used by Sernander (1912,
1917) and Degelius (1939). “Species restricted to seashores, directly
influenced by seawater, either by waves or spray, are marine. Species living
above the marine zone, influenced by airborne salt, but not the saltwater
itself, are maritime” (Arup, 1995b).

Living in
a marine environment, C. coralloides is also often exposed to salt
spray, high humidity and periods of foggy weather. Lichens can absorb moisture
directly out of the air through their thallus. This also means that lichens
are very affected by salt exposure from saltwater spray. In fact, the main
factor that influences local distribution of maritime lichens is the amount
of salt spray they are exposed to. Another important determining factor
is the amount of light exposure.

The main cortical pigment in C. coralloides is parietin, an anthraquinone
that functions as a sunscreen for the lichen. Studies have been done
on Xanthoria parietina, another lichen that has parietin as a major
cortical pigment, exploring the photoprotectant qualities of parietin for
the lichen. Parietin absorbs light in the blue light and UV range
(Gauslaa, 2003). It therefore makes sense that C. coralloides is
an orange lichen. Those are the light waves that it is reflecting! Both
blue light and UV light are high frequency waves and protection from them
is important for lichens such as C. coralloides that live in very
light exposed sites.

C. coralloides lives mainly in the lower part of the supralittoral
zone on exposed rock surfaces, and is therefore sometimes exposed to
intense levels of irradiation. C. coralloides grows mostly
on vertical or somewhat vertical surfaces. It is possible that this
preference helps lower the amount of photodamage sustained by the lichen.
The C. coralloides in this picture is growing on a North West
facing rockface at the Hopkings Marine Station in Monterey. There is
conspicuously no C. coralloides growing on the opposing rockface,
which, due to its more southerly orientation, gets more sun. The majority
of the C. coralloides growing at Hopkins followed this trend.
It is possible that this selection of North facing substrate is a technique
for reducing photodamage along with the selection of more verticle surfaces.

C. coralloides is similar in many respects to another rock dwelling
species of Caloplaca, Caloplaca brattie. However,
unlike Caloplaca brattiae, C. coralloides avoids rocks
covered in bird excrement.

At the Hopkins Marine Station in Monterey, C. coralloides lives
on weathered granite, which is rich in silicates. Chemically different types
of rock often have different lichen flora; however, lichens do not absorb
nutrients or minerals from their substrate through their rhizoids. Perhaps
a lichen prefers a particular substrate because it can absorb minerals
from rainwater that runs over the substrate and part of the thallus.
Or, perhaps the specific mineral content or the pH of a particular substrate
is more conducive to the survival of a lichens photobiont in early stages
of growth or helps with the germination of that lichen’s spores.

There are lichens distributed on all continents. However, C. coralloides is
endemic to the west coast of N. America. 20 species of Caloplaca live
on seashore rocks in continental N. America. C. coralloides ranges
from Baja California Norte to Oregon. Just north of this northern limit
there are not suitable rock substrates for C. coralloides to
grow on. Because C. coralloides is rock-dwelling it is
restricted to coastal regions with rocks, glacial boulders or pebbles.
A possible reason why C. coralloides and other marine and maritime
lichens do not grow on arctic shorelines is that there is too much ice
scouring (Brodo).

Photosynthesis in lichens proceeds best at 50-70% water saturation while
respiration happens at highest rates when the lichen is completely or almost
completely saturated with water. Therefore, dried out lichen do not photosynthesize
or respire very much, and are somewhat dormant. This condition does not
permanently damage most lichens. When returned to metabolically activating
conditions, within a short time lichens can resume metabolizing.

The optimal levels of irradiation for photosynthesis differ depending on
the photobiont. Green algal photobionts, such as that in C. coralloides,
function better under higher levels of irradiance than do cyanobacteria.